Dc voltage converting device

ABSTRACT

A DC voltage converting device is on the output side connected to a DC voltage source and, on the output side, supplies a converted DC voltage to at least one electrical consumer via a cable connection. To improve such a DC voltage converting device in that also with high DC voltages on the input side, a conversion into another DC voltage is possible without any special constructional efforts and high costs while complicated cooling means or the like, are avoided at the same time, the Dc voltage converting device comprises a plurality of DC voltage converting units of which each is serially connected to the DC voltage source on the input side and connected in parallel with the cable connection on the output side for supplying the converted DC voltage.

[0001] A DC voltage converting device is connected to a DC voltagesource on the input side. On the output side, the converting devicesupplies a converted DC voltage to at least one electrical consumer.

[0002] Such DC voltage converting devices are in particular used infields where DC voltages must be converted and/or stabilized. Typicalapplications are e.g. photovoltaic installations, the automotiveindustry, direct-current traction drives for subways and streetcars,household drives for hair dryer, drilling machine, or the like,telecommunications and also semiconductor technology.

[0003] If a high DC voltage is present on the input side, acorresponding conversion into another DC voltage is difficult as a rulebecause corresponding components of the converting device do not show asufficiently high breakdown strength. Moreover, in the case of a highpower to be transmitted, the heat developed in the converting device maybe considerable even if the power loss is only 10 or 20%. To be able todischarge the power loss converted into heat, corresponding coolingmeans must be provided. This makes the converting device more expensiveand also larger due to the additional cooling means.

[0004] It is therefore the object of the present invention to improve aDC voltage converting device of the above-mentioned type such that alsowith high DC voltages on the input side a conversion into another DCvoltage is possible without any special constructional efforts and highcosts while complicated cooling means, or the like, are avoided at thesame time.

[0005] In connection with the features of the preamble of patent claim1, this object is achieved in that the DC voltage converting devicecomprises a plurality of DC voltage converting units of which each isserially connected to the DC voltage source on the input side andconnected in parallel with the cable connection on the output side forsupplying the corresponding DC voltage for the electrical consumer.

[0006] Due to the use of the converting units and the special wiringwith respect to the DC voltage source, each unit converts only part ofthe high DC voltage applied. For instance, if there is a DC voltage of6000 V on the input side, each of the converting units will only convertthe nth fraction of the input voltage if these are of an identicalconstruction and on condition that there is a number of n convertingunits. For instance, if n is 30, each converting unit would only convert200 V. The breakdown strength of the corresponding components of theconverting units is normally considerably higher than 200 V, so thatthere is no risk in this respect.

[0007] On the output side, depending on the design of the convertingunits and with a corresponding wiring to the cable connection, it ise.g. possible to provide a value of 300 V for the electrical consumer.

[0008] Of course, it is possible to use different numbers of convertingunits, the number following e.g. from the high DC voltage applied on theinput side, from the output voltage needed by the electrical consumer,or the like. It is also possible that the converting units are of nosimilar construction, but convert e.g. different amounts of the inputvoltage per converting unit into a corresponding output voltage.However, for reasons of maintenance and repair, it is of greateradvantage to give all converting units an identical design.

[0009] Moreover, it is ensured through the number of the convertingunits that, when one, two, three or even more converting units fail, acomplete failure of the voltage supply to the electrical consumer neednot be feared (redundancy). Instead of this, the converting units thatare still operative can receive more voltage on the input side andconvert the same into the output voltage required.

[0010] A further advantage of the use of a plurality of converting unitsis that even with increased powers in the kW range of e.g. 6000 volt and1, 2, 3 or more amp, the power loss of the converting device isdistributed over the corresponding converting units. Heat correspondingto the power loss is thus not generated pointwise and within a confinedspace, but the heat is generated such that it is substantially evenlydistributed over all converting units. This simplifies the coolingprocess considerably and, as a rule, just requires a simple air coolingor no further cooling than by the environment, depending on therespective arrangement of the converting units.

[0011] For instance, the converting units may be spaced apart from oneanother such that they do not mutually affect one another in their heatdevelopment, and each converting unit can thus be cooled separately.

[0012] Depending on the number and design of the converting units, DCvoltages of about 1 kV to 10 kV and, in particular, 3 kV to 8 kV may bepresent on the input side. It should once again be pointed out that evenhigher input voltages with a correspondingly high power can be convertedif the number of the converting units or their correspondingconstruction is matched accordingly. Attention must here above all bepaid that the breakdown strength of the components of every convertingunit is at least so high that the amount of the input voltage to beconverted by the converting unit is smaller than the breakdown strength.

[0013] To be able to receive the DC voltages without any great loss orinterference also over large distances from the DC voltage source, theDC voltage converting device may be connected via a coaxial cableconnection to the DC voltage source. Even at high DC voltages and highpowers, such a coaxial cable connection may have a small cross-section,whereby the costs are considerably reduced, for instance, in comparisonwith an AC voltage supply. Moreover, a coaxial cable connection is wellsuited also for data transmission in addition to transmitting electricalpower. As for a DC voltage transmission, attention must further be paidthat there are only conductor losses and no attenuation losses inaddition, as is the case with the transmission of AC voltage.

[0014] To be able to transmit data sent via the cable connection in thedirection of the DC voltage source, i.e. without interference and at ahigh speed, the DC voltage converting device may comprise a filter meansarranged upstream on the input side.

[0015] To use highly efficient converting units that, consequently, onlygenerate a small amount of heat and thus ensure a high reliability and,economically speaking, are excellent in production and operation at thesame time, a corresponding DC voltage converting unit may be designed asa clocked switch mode power supply. In comparison with e.g. linearcontrolled power supplies, these offer the further advantage that theyshow a small volume, a reduced noise development, reduced smoothingdemands and an increased input voltage range.

[0016] The switch mode power supplies are subdivided into primarily andsecondarily clocked or switched ones. To ensure an electrical isolationbetween input and output of the converting device, the switch mode powersupply may preferably be clocked (switched) primarily.

[0017] If, in particular, high output powers are to be generated in thekW range, the switch mode power supply may be designed as a push-pullconverter. Such a converter is further characterized by a lower currentload of its semiconductor components, an easy adjustability of theoutput voltage, high efficiency and a small transformer as thetransforming means.

[0018] Such a push-pull converter may be designed as a half-bridge orfull-bridge push-pull converter. In particular for maximum powers theswitch mode power supply may be designed as a full-bridge push-pullconverter.

[0019] A switching means for correspondingly switching the transformerof the switch mode power supply may e.g. be designed as a switchingtransistor, in particular a power MOSFET or BIMOSFET. It is alsopossible that the switching means is designed as a thyristor.

[0020] In a push-pull converter, at least two switching transistors areused that operate in the push-pull mode. Advantageously, it is alsopossible to operate in the push-pull mode with a clock ratio of 1:1.This means that both switching transistors are each switched throughalternatingly for the same periods of time.

[0021] To obtain an output voltage that is as smooth as possible and hasa relatively small amount of harmonics, the switch mode power suppliesof the DC converting device may be clocked in synchronism. This meansthat all switch mode power supplies are clocked at the same clock rate.

[0022] To increase a cutoff frequency of the system as much as possiblewith respect to interferences of the DC voltage on the secondary side,the switch mode power supplies of the DC converting device may beclocked with respect to one another in phase-shifted fashion.

[0023] To produce corresponding harmonics only to a small degree in thisconnection, a phase shift in the clocking of neighboring switch modepower supplies may be 1/n each if n is the number of the switch modepower supplies of the DC voltage converting device. Hence, the phaseshift is such that the n+1th switch mode power supply would be again inphase with the first switch mode power supply (cyclic phase shift).

[0024] To transmit also data in particular via the coaxial cableconnection to the DC voltage source, a data signal coupling/decouplingmeans may be arranged upstream of the filter means in the direction ofthe DC voltage source. Said means serves the communication with the DCvoltage source that is possibly far away and with all of the furthermeans located there. This communication connection also serves tomonitor, control and, optionally, regulate the components of the DCvoltage converting device and the electrical consumers connectedtherewith via the cable connection.

[0025] To monitor, control and regulate the corresponding components ofthe DC voltage converting device on site, a controller may be assignedat least to the DC voltage converting device and the components thereof.However, the controller may also be responsible for electrical consumerssupplied by the converting device with DC voltage and may monitor thesame in their function and carry out the control or regulation of theconsumers.

[0026] To ensure an undisturbed transmission of a communicationconnection in this respect and to scan the DC voltage on the input sidesubstantially completely at the same time, the clock rate of the switchmode power supply may be in the range of 10 kHz to more than 1 MHz and,in particular, in the range of 50 kHz to 300 kHz.

[0027] In this connection each switch mode power supply can e.g. bereadjusted in its output voltage via changes in the duty factor, inparticular, in case of failure of another switch mode power supply ofthe DC voltage converting device.

[0028] In the simplest case a readjustment of the output voltage of aswitch mode power supply can take place via a change in the duty factorof the switching transistor.

[0029] To control the switching transistors accordingly, the switch modepower supply may comprise a pulse modulation means for the clockedcontrol of the switching transistors, the pulse modulation meanssupplying a sequence of pulses of a variable width and/or height and/orfrequency for clocking the switching transistors.

[0030] In connection with the filter means, it should additionally bementioned that said means filters, in particular, the frequency rangewithin which the communication connection to the DC voltage source takesplace. This means that only a lower frequency range of up to e.g. 50 kHzis filtered. Relatively simple and inexpensive filters are thussufficient.

[0031] The controller used according to the invention can be designed inits monitoring function such that it monitors e.g. the individual switchmode power supplies, reports on the failure of corresponding switch modepower supplies and the location of said switch mode power supplieswithin the DC voltage converting device and sends an alarm message incase of failure of a predetermined number of switch mode power supplies.The corresponding information of the controller can be transmitted viathe coaxial cable connection to the DC voltage source that is locatedfar away, and can be represented there accordingly.

[0032] An advantageous embodiment of the invention shall now beexplained in more detail in the following with reference to the figuresattached to the drawing, in which:

[0033]FIG. 1 is a block diagram of an embodiment of the DC voltageconverting device according to the invention;

[0034]FIG. 2 shows a basic embodiment of a switch mode power supply foruse in the DC voltage converting device according to FIG. 1;

[0035]FIG. 3 shows a full-bridge push-pull converter as the switch modepower supply according to FIG. 2; and

[0036]FIG. 4 shows a half-bridge push-pull converter as the switch modepower supply according to FIG. 2.

[0037]FIG. 1 is a schematic illustration showing an embodiment of the DCvoltage converting device 1 according to the invention.

[0038] The converting device 1 comprises a plurality of DC convertingunits 5 in the form of switch mode power supplies 8. These are wired oneafter the other on the input side and connected to a DC voltage source 2via a coaxial cable connection 6. The DC voltage source 2 may bearranged at a remote place; the length of the coaxial cable connection 6may here be several kilometers, for instance 50, 60 or more kilometers.

[0039] A filter means 7 is arranged upstream of the DC voltageconverting units 5. This means filters, in particular, a frequency rangeneeded for a communication connection to the DC voltage source 2. Thefiltering operation may e.g. be carried out within a frequency range ofup to 50 kHz.

[0040] The DC voltage converting units 5 and the corresponding switchmode power supplies 8, respectively, are wired in parallel with oneanother on their output side and connected accordingly with a cableconnection 4. The cable connection 4 leads to at least one electricalconsumer 3.

[0041] Such an electrical consumer may e.g. be an actuator for a meansfor controlling a fluid flow into a fluid line or within the fluid line.Such means are e.g. valves, shut-off devices for emergency cases, suchas leakage, pipe breakage, or the like, throttles, pumps, etc. Thesemeans and the actuators assigned to them are possibly disposed in roughterrain that is difficult to reach. The means and actuators may also bearranged underwater. The fluid can enter into the ducts at a highpressure and be guided therealong. Moreover, the fluid may be aggressiveor pollute the environment, so that a corresponding monitoring andcontrol of the fluid flow is of utmost importance.

[0042] The means and the actuators assigned to them, as well as the DCconverting device, may be arranged below sea level. The coaxial cableconnection can be laid up to the water surface to the corresponding DCvoltage source. It is also possible that means and actuators arearranged on the surface of the earth at a place that is difficult toreach, and are controlled and monitored accordingly from a remote place.

[0043] A controller 17 is assigned at least to the DC voltage convertingdevice 1 for monitoring, controlling and regulating the correspondingmeans. This controller can also monitor, control or regulate theelectrical consumer(s) 3.

[0044] For the transmission of corresponding data to the remote DCvoltage source 2 and means further assigned to said source, a datacoupling/decoupling means 16 may be provided. This means is arrangedupstream the filter means 7 between filter means 7 and DC voltage source2. Corresponding data signals can be coupled and decoupled, forinstance, by the controller 17 into and out of the coaxial cableconnection 6 via the data coupling/decoupling means. A communicationconnection is thereby established between DC voltage source 2 and themeans assigned thereto and also the DC voltage converting device 1 andthe electrical consumers 3 supplied by the device. The communicationconnection is bidirectional, so that data can be exchanged in bothdirections via the coaxial, cable connection 6 and with the controller7.

[0045]FIG. 2 is a simplified illustration showing an embodiment of aswitch mode power supply 8 for use for the DC voltage converting units 5according to FIG. 1.

[0046] The switch mode power supply 8 is formed by a push-pull converter9. Said converter is serially connected with further push-pullconverters on its input side to corresponding input terminals 26 and 28.The push-pull converter 9 comprises an input capacitor 25 and atransformer 24 which are wired accordingly with the input terminals 26and 28. The transformer 24 comprises a primary winding and a secondarywinding that are coupled magnetically. The primary winding is connectedin parallel with the input capacitor 25.

[0047] The primary winding is controlled and clocked accordingly via aswitching means 11 of the push-pull converter 9. Said switching means 11is formed by one or several switching transistors, see FIGS. 3 and 4.Preferably, such a switching transistor is designed as a power MOSFET,BIMOSFET or thyristor. For the purpose of simplification FIG. 2 showsthe switching means 11 symbolically by way of a switch corresponding tofour switching transistors and two switching transistors, respectively,in the embodiments shown in FIGS. 3 and 4.

[0048] The secondary winding is wired via a diode 20 and a load 21 to anoutput terminal 29. The load 21 may e.g. be an inductor 23, see FIGS. 3and 4. A smoothing capacitor 22 is connected in parallel with thesecondary winding.

[0049] The output terminal 29 and the corresponding output terminals 29of the further switch mode power supplies 9 and the push-pull converters9, respectively, are wired in series with one another and connected tothe cable connection 4; see FIG. 1.

[0050] The further output terminal 30 on the secondary side of thepush-pull converter 9 is wired with the also further output terminals 30of the other push-pull converters in series with ground 31.

[0051]FIGS. 3 and 4 show two detailed embodiments of a push-pullconverter 9.

[0052] The push-pull converter according to FIG. 3 is designed as afull-bridge push-pull converter 10.

[0053] In this converter, the switching means 11 is formed by fourswitching transistors 12, 13, 14 and 15. Two of the switchingtransistors are respectively combined and serve in pairs to supply theinput voltage from the DC voltage source 2 to the primary winding, thepairs of switching transistors being controlled in the push-pull mode.The push-pull mode takes place such that the duty factor of the twopairs is 1:1 each time.

[0054] A pulse modulation means 18 is provided for the clocked controlof the switching transistors. This means supplies a sequence of pulsesthat are variable in their width and/or height and/or frequency.

[0055] The pulse modulation means 18 is realized by a correspondingelectronic circuit that is known per se.

[0056] It is possible that the duty factor is changed on the primaryside and thus the corresponding output voltage. This takes e.g. placewhenever one or several of the push-pull converters 9 have failed.Despite failure of a number of push-pull converters the desired voltagecan still be supplied on the output side by the remaining push-pullconverters through a corresponding control of the duty factor and anincrease in the output voltage of the remaining push-pull converters. Toregulate the output voltage, said voltage can be tapped continuously atthe output, possibly amplified and supplied to the pulse modulationmeans via an optocoupler for electrical isolation.

[0057] In the further embodiment of the push-pull converter according toFIG. 4, said converter is designed as a half-bridge push-pull converter19. In this case, essentially two switches are formed by a switchingtransistor. These switch the primary winding to the input voltagealternatingly in push-pull mode and non-overlapping fashion. Thecorresponding diodes on the output side are also conductive inalternating fashion.

[0058] The transformer 24 operates without direct current because of thesymmetrical operation. This, however, is only the case if the ON periodsof the switching transistors are exactly the same. This can beaccomplished through a corresponding control by the pulse modulationmeans 18, which is not shown in FIGS. 2 and 4 for the sake ofsimplification.

1. A DC voltage converting device which, supplies a converted DC voltageto at least one electrical consumer via a cable connection, the DCvoltage converting device comprising: a plurality of DC voltageconverting units of which each is serially connected to a DC voltagesource on an input side and connected in parallel with the cableconnection on an output side for supplying the converted DC voltage tothe at least one electrical consumer.
 2. A DC voltage converting deviceaccording to claim 1, wherein a DC voltage from the DC voltage sourceapplied on the input side of the DC voltage converting units is in theorder of about 1 kV to 10 kV.
 3. A DC voltage converting deviceaccording to claim 1, wherein the cable connection comprises a coaxialcable.
 4. A DC voltage converting device according to claim 1 whereinthe DC voltage converting device further comprises a filter on the inputside of the DC voltage converting units.
 5. A DC voltage convertingdevice according to claim 1 wherein each DC voltage converting unit isdesigned as a clocked switch mode power supply.
 6. A DC voltageconverting device according to claim 5 wherein the switch mode powersupply is primarily clocked.
 7. A DC voltage converting device accordingto claim 5 wherein the switch mode power supply is designed as apush-pull converter.
 8. A DC voltage converting device according toclaim 5 wherein the switch mode power supply is designed as afull-bridge push-pull converter.
 9. A DC voltage converting deviceaccording to claim 5 wherein the switch mode power supply comprises oneor more switching transistors selected from the group consisting ofpower MOSFETs transistors and power BIMOSFETs transistors.
 10. A DCvoltage converting device according to claim 9 wherein the one or moreswitching transistors are clocked in push-pull fashion at a clock ratioof 1:1.
 11. A DC voltage converting device according to claim 5 whereinthe switch mode power supplies of the DC voltage converting device areclocked in synchronism.
 12. A DC voltage converting device according toclaim 5 wherein the switch mode power supplies of the DC voltageconverting device are clocked in phase-shifted fashion relative to oneanother.
 13. A DC voltage converting device according to claim 12wherein a phase shift associated with a clocking of neighboring switchmode power supplies comprises a phase shift of 1/n if n is the number ofthe switch mode power supplies of the DC voltage converting device. 14.A DC voltage converting device according to claim 4 wherein a datacoupler/decoupler is arranged upsteam of the filter in the direction ifthe DC voltage source.
 15. A DC voltage converting device according toclaim 14 further comprising a controller that is assigned to one or morecomponents selected from the group consisting of the DC voltageconverting units, the filter, and the data coupler/decoupler.
 16. A DCvoltage converting device according to claim 5 wherein a clock frequencyof the switch mode power supply is within the range of 50 kHz to 300kHz.
 17. A DC voltage converting device according to claim 9 wherein anoutput voltage of each switch mode power supply is readjustable in caseof failure of another switch mode power supply of the DC voltageconverting device.
 18. A DC voltage converting device according to claim17 wherein a duty factor of the one or more switching transistors isvariable for readjusting the output voltage of a switch mode powersupply.
 19. A DC voltage converting device according to claim 9 whereinthe switch mode power supply comprises a pulse modulator that isoperable to output a sequence of variable pulses for clocking the one ormore switching transistors.
 20. A system for supplying power to anelectrical device, the system comprising: a DC source; a plurality ofDC/DC converters, wherein inputs of the DC/DC converters are connectedto the DC source via an electrical conductor and wherein outputs of theDC/DC converters provide a converted DC voltage to the electricaldevice, wherein the plurality of DC/DC converters receive a high DCvoltage from the DC source via the electrical conductor and convert thehigh DC voltage to a lower DC voltage without a cooling mechanism thatwould otherwise be needed when less than the plurality of DC/DCconverters are implemented to convert the high DC voltage to the lowerDC voltage.
 21. The system of claim 20 further comprising a controllercoupled to each of the DC/DC converters to regulate one or morefunctions of each DC/DC converter.
 22. The system of claim 21 whereinthe controller is coupled to the electrical device to regulate one ormore functions of the electrical device.
 23. The system of claim 22further comprising a data coupling device coupled to the electricalconductor and the controller, wherein the data coupling device isoperable to decouple data from the electrical device and provide thedata to the controller while power is supplied to the electrical device.24. The system of claim 23 wherein the data coupling device couples datafrom the controller to the electrical conductor while power is suppliedto the electrical device.
 25. The system of claim 22 wherein thecontroller detects a failure of a DC/DC converter and causes other DC/DCconverters to compensate for the failed DC/DC converter.
 26. The systemof claim 21 wherein the controller independently controls an outputpower of each DC/DC converter.
 27. The system of claim 20 wherein theDC/DC converters are in a spaced relationship with each other such thatheat from the DC/DC converters is dissipated without the coolingmechanism.
 28. The system of claim 26 wherein each DC/DC convertercomprises a switching mechanism that permits the output power of eachDC/DC converter to be controlled using a pulse width modulated signal.29. The system of claim 24 wherein the data decoupled from theelectrical conductor is used to control the electrical device.
 30. Thesystem of claim 24 wherein the data coupled to the electrical conductoris used to monitor the electrical device.
 31. The system of claim 24wherein the data coupled to the electrical conductor is used to monitorthe DC/DC converters.
 32. The system of claim 20 further comprising afilter coupled between the DC source and the DC/DC converters.
 33. Thesystem of claim 20 wherein the electrical device is an actuator.
 34. Thesystem of claim 20 wherein the electrical conductor is a coaxial cable.35. The system of claim 34 wherein the electrical condouctor is underwater.
 36. The system of claim 35 wherein the electrical conductor is atleast one kilometer in length.
 37. A system for supplying power from asea surface to a subsea location, the system comprising: an DC sourcefor disposal at the sea surface; a subsea electrical device; and aplurality of DC voltage converters for disposal subsea, each having aninput side connected to the DC source via an electrical conductor and anoutput side connected to the subsea electrical device.
 38. The system ofclaim 37 wherein the electrical conductor extends subsea to the subseaelectrical device.
 39. The system of claim 37 wherein a frequency filteris placed between the DC source and the input side of each DC voltageconverter.
 40. The system of claim 37 wherein the DC converters are in aspaced relationship with each other such that heat from the DCconverters is dissipated without the need of a cooling component. 41.The system of claim 37 further including a controller which detects afailure of a DC converter and causes other DC converters to compensatefor the failed DC converter.
 42. A system for supplying power to aremote electrical device, the system comprising: a DC source; aplurality of DC voltage converters each having an input seriallyconnected to the DC source and each having an output connected inparallel to the remote electrical device via a conductor, wherein thelength of the conductor is at least one kilometer.